Since this is the BBing section I assume you're more concerned with size than strength but nevertheless I will point out that for strength 5 days a week will be preferable to two - but still if it were strength I think I'd rearrange the exercises anyway.

For mass, I don't think there's a lot to choose between them, though I'm still inclined to go for 5 days rather than 2 because of the more regular stimulus. I agree that some kind of alternation could work well - but I think I'd extend to at least 4 weeks on one before switching to the other.